The present invention is related to venous return cannulas for cardiopulmonary bypass to an extracorporeal heart-lung circuit.
In most cardiopulmonary bypass techniques, the preferred area of insertion for the venous return cannula is the appendix of the right atrium. The auricular appendix is convenient for clamping purposes and is conveniently located for cannulation. In fact, the auricular appendix has at times been referred to as "God's gift to the heart surgeon".
Many forms of cardiopulmonary bypass techniques involve the use of more than one venous return line. The appendix can accept only one cannula while the other must be inserted through an incision made elsewhere in the atrium. The double incision requires placement of two separate sutures for snaring the cannulas after insertion. All this preparation takes valuable time and increases the chances for later complication. The two cannulas interfere with critical surgical procedures and in doing so, further increase the overall time required to complete the surgery.
It becomes desirable, since the venous drainage cannulas lead into the same phlebotomy line of the extracorporeal circuit, to use a single cannula inserted through a single incision in the atrium appendix. This has not been possible, however, because it often becomes necessary to clamp or "tape" the inferior and superior vena cavae about the cannulas, preventing flow of blood into the right atrium. The physical separation of the vena cavae prohibit such practice with a single tubular cannula.
The typical double cannula arrangement is shown in U.S. Pat. No. 3,903,895 to R. D. Alley et al. FIG. 4 of Alley's drawings show a venous return line of an extracorporeal circuit with a double tubular end, one cannula end is inserted through an incision in the atrium and is extended upwardly into the superior vena cava (SVC). The remaining cannula is inserted through a second, separate incision and is directed downwardly into the inferior vena cava (IVC). The two branches extend outwardly of the heart to connect with converging lines of the extracorporeal heart-lung circuit.
An infusion cannula is typically inserted into the aorta, further obstructing the operative area. The three protruding tubes, though flexible, hinder positioning of the heart to facilitate aortocoronary bypasses, valve implants, etc. In addition, the three tubes hinder direct access by the various surgical instruments used in such heart operations.
U.S. Pat. No. 3,835,863 to Goldberg et al discloses a "T" tube that is used as a catheter for implantation in an internal duct for drainage. The transverse arms of the "T" tube are slotted longitudinally to enable folding over one another to the diameter of the main tube branch. The tubes can thus be folded onto one another and inserted through an incision in the associated duct. Upon insertion, the tube branches may spring apart, opening into the duct. Withdrawal of the tube is accomplished simply by pulling the tube outwardly. The transverse branches of the tube will fold together at the incision as the tube is pulled outwardly.
The Goldberg "T" tube may have beneficial use in drainage of internal ducts such as the bile ducts in abdominal surgery. However, such a drainage tube would not be functional for use as a venous return cannula, due to the open slots formed along the tube branches. Furthermore, the open tubes would not lend themselves to operation with an inside or outside obturator by which the branch ends could be accurately guided as they are inserted or withdrawn from the incision.